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JC 9118 



Bureau of Mines Information Circular/1986 



Face Ventilation for Oil Shale Mining 



By Edward D. Thimons, Carl E. Brechtel, Marvin E. Adam, 
and Joseph F. T. Agapito 



UNITED STATES DEPARTMENT OF THE INTERIOR 



{riJdmu. u*** 



T 

Information Circular 9118 

vi A 




Face Ventilation for Oil Shale Mining 



By Edward D. Thimons, Carl E. Brechtel, Marvin E. Adam, 
and Joseph F. T. Agapito 




UNITED STATES DEPARTMENT OF THE INTERIOR 
Donald Paul Hodel, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 







Library of Congress Cataloging in Publication Data: 



Face ventilation for oil shale mining. 

(Bureau of Mines information circular : 9118) 

Bibliography: p. 21-22 

Supt. of Docs, no.: I 28.27: 9118. 

1. Mine ventilation. 2. Oil-shales. I. Thimons, Edward D. U. Series: Information circular 
(United States. Bureau of Mines) ; 9118. 

TN295.U4 [TN301] 622 s [622'.42] 86-600361 



CONTENTS 



Page 



Abstract 1 

Introduction 1 

Acknowledgments 2 

Face ventilation requirements 2 

Diesel engine emissions 3 

Oil shale dust and diesel particulates 4 

Blasting 5 

Methane occurrence in oil shale raining 6 

Sudden inflow of methane-saturated water or free methane 7 

Blast-released methane 8 

Maximum length of deadheading 9 

Fan system design 9 

Design of the jet fan system 9 

Phases 1 and 2 10 

Phase 3 10 

Phase 4 10 

Design of the ducted fan system 12 

Applications of tracer gas testing results 12 

Tracer gas determination of dilution efficiencies 13 

Test results 14 

Impact of fan recirculation 15 

Impact of fan outlet locations 15 

Case studies of performance in projected operating conditions 17 

Blast-produced pollutants 17 

Diesel emissions 18 

Methane emissions 18 

General conclusions on face ventilation 20 

References 21 

ILLUSTRATIONS 

1. Ventilation velocities required to achieve methane layering numbers of 2 

and 5 versus methane inflow 8 

2. Typical curve of methane concentration in exhaust air after blasting oil 

shale in the saline zone at Horse Draw 9 

3. Schematic of dead-end heading ventilated by jet fan 9 

4. Plan view of freely expanding turbulent jet illustrating McElroy's dif- 

ferent phases of velocity decay 10 

5. Approximate distance to transition zone (phase 4 flow) as a function of 

outlet velocity normalized to outlet diameter for fans located adjacent 

to a wall 11 

6. Jet fan penetration versus velocity curve for large jet fan tested in oil 

shale mining 11 

7. Schematics of the ducted fan system operating in deadheading 12 

8. Schematic of Colony Mine showing mine ventilation system and location of 

test room in crosscut 7 13 

9. Test room grid system showing location of fans during tracer gas tests.... 14 

10. Schematic showing tracer gas sampling points and tracer gas release point 

for various simulations 15 

11. Ducted system operating in blowing mode with jet fan to assist methane 

plume mixing 20 

12. Reorientation of jet fan to minimize inlet recirculation and reduce 

effective room airflow rate for methane dilution 20 



TABLES 



Page 



1. Threshold limit values of air pollutants expected in oil shale mining.... 2 

2. Comparison of engine exhaust production and required ventilation 3 

3. Comparison of measured respirable dust concentration and TLV 4 

4. Quartz content of dust sample collected during simulated loading 

operations 5 

5. Estimated proportions of oil shale dust, diesel particulates, and pro- 

jected production rates 5 

6. Comparison of estimated and measured concentration of gases produced by 

full-face blast at Colony pilot oil shale mine 6 

7. Summary of publicly available data on methane occurrence in oil shale.... 6 

8. Comparison of dilution efficiencies measured in tracer gas tests 14 

9. Potential increase in dilution efficiency resulting from elimination of 

inlet recirculation 16 

10. Locations, orientations, and face air velocities for jet fan 16 

11. Duct discharge locations and face sweep velocities for the ducted 

fan-blowing 16 

12. Estimated time to clear blast-produced pollutants to TLV's 17 

13. Comparison of required fan outlet flow rates 18 





UNIT OF MEASURE ABBREVIATIONS 


USED IN 


THIS REPORT 


bhp 


brake horsepower 


hp 


horsepower 


Btu/h 


British thermal unit per 
hour 


in 


inch 






in w.g. 


inch, water gauge 


ft 


foot 










lb 


pound 


ft 2 


square foot 










lb/ft 3 


pound per cubic foot 


ft 3 


cubic foot 










mg/m 3 


milligram per cubic meter 


f t/min 


foot per minute 










mg/min 


milligram per minute 


ff min/ ft 


foot per minute per foot 










min 


minute 


ft 3 'min/bhp 


cubic foot per minute 








per brake horsepower 


Um 


micrometer 


ft 3 /st 


cubic foot per short ton 


pet 


percent 


gal 


gallon 


ppm 


part per million 


h 


hour 


ppt 


part per trillion 



FACE VENTILATION FOR OIL SHALE MINING 

By Edward D. Thimons, 1 Carl E. Brechtel, 2 Marvin E. Adam, 3 and Joseph F. T. Agapito 4 



ABSTRACT 

This Bureau of Mines report presents expected levels of air pollu- 
tants in the face areas of oil shale mines, based upon data collected by 
the authors and previous investigators. Ventilation requirements to 
maintain these pollutant levels below their threshold limit values and 
Federal and local mine air quality standards are discussed. Two practi- 
cal face ventilation systems are discussed in terms of actual in-mine 
test experience. 

INTRODUCTION 

Oil shale mine entries typically will have cross-sectional areas of 
1,500 ft 2 or more. Face ventilation systems, to effectively dilute and 
remove pollutants from the face area of these mines, will be critical to 
the successful operation of the underground oil shale industry. The 
large diesel-powered equipment and heavy face blasting needed in oil 
shale mines create substantial ventilation requirements. Furthermore, 
it is possible that some oil shale mines will be classified as gassy, 
which will introduce additional ventilation problems and requirements. 

For ventilation personnel to deal with these problems, they must un- 
derstand the levels of pollutants to be expected and the threshold limit 
values (TLV's) of these pollutants. It will also be most helpful to 
them to have some knowledge of what face ventilation systems have 
already been tested and of how these systems performed. The purpose of 
this report is to provide this information. 

Under a Bureau of Mines contract, J. F. T. Agapito & Associates con- 
ducted a detailed study to establish face ventilation requirements for 
oil shale mines, design face ventilation systems to satisfy these 
requirements, and test and evaluate the most promising of these designs 
in an oil shale mine. The information presented in this report was 
obtained under that program. 

Supervisory physical scientist, Pittsburgh Research Center, Bureau of Mines, 
Pittsburgh, PA. 

■"•Associate, J. F. T. Agapito & Associates, Inc., Grand Junction, CO. 
^Senior engineer, J. F. T. Agapito & Associates, Inc. 
4 President, J. F. T. Agapito & Associates, Inc. 



ACKNOWLEDGMENTS 



The authors wish to acknowledge both 
the technical and financial contributions 
to this work provided by the Colorado 
Mining Association and the U.S. Depart- 
ment of Energy, who acted as joint spon- 
sors of this work with the Bureau of 
Mines. Special thanks are directed to 
the following members of the Oil Shale 
Advisory Committee of the Colorado Mining 



Association: David Cole, president, Col- 
orado Mining Association; L. A. Weakly, 
Exxon Co., USA — Committee Chairman; Sam 
Vera, Mobil Oil Co.; David Starbuck, 
White River Shale Oil Corp.; John Shaler, 
Cathedral Bluffs Shale Oil Co.; Alan 
Salter, Union Oil Co. of California; and 
Dr. Art Hartstein, U.S. Department of 
Energy. 



FACE VENTILATION REQUIREMENTS 



This section reviews background data on 
mine air pollutant production to help 
establish air quantities. The quality of 
air at the face must meet regulatory re- 
quirements. In some cases, there may be 
multiple requirements. For example, Col- 
orado State law requires that 75 ft 3 /min 
of fresh air be used to ventilate each 
brake horsepower of engine capacity; it 
also requires the maintenance of TLV's 
for various air pollutants, as specified 
by the Mine Safety and Health Administra- 
tion (MSHA). The main sources of air 
pollutants expected to impact face venti- 
lation requirements follow: 

Loading operations . — Noxious gases, 
diesel particulates, and dust are pro- 
duced during loading operations at the 
face. These are especially severe for 



mines designed for front-end loaders with 
truck haulage. 

Blasting . — Large quantities of noxious 
gases and dust are generated by face 
blasting. 

Strata gas . — Methane can occur both as 
free gas in solution with groundwater and 
as absorbed gas In solid solution with 
the kerogen in oil shale. The existence 
of methane has not been reported for 
properties at the southern rim of the 
Piceance Creek Basin, but it has been 
observed during development mining in the 
Uinta Basin and central portion of the 
Piceance Creek Basin. 

Specific air pollutants of concern pro- 
duced during oil shale mining and their 
allowable concentrations or TLV's are 
listed in table 1. These values are 



TABLE 1. - Threshold limit values of air pollutants 
expected in oil shale mining 



Pollutant 



TLV 



Exposure 
criterion 



Maximum 
excursion 



C0 2 
CO. 
NO. 



.ppm. 
.ppm. 
.ppm. 



N0 2 ppm. 

Formaldehyde ppm. 

H 2 S ppm. 

Methane ppm. 

Respirable dust 2 mg/ra 3 . 

Total dust mg/m 3 . 



5,000 

50 

25 

5 

2 

10 

10,000 

1.4-0.7 

3.6-1.9 



TWA 
TWA 
TWA 
C 

c 

TWA 
C 

TWA 
TWA 



ND 

75 

37.5 

5 

2 

20 

10,000 

ND 

ND 



C Maximum value not to be exceeded. 

ND Not defined. 

TWA Time-weighted average. 

1 Based upon American Conference of Governmental Indus- 
trial Hygienists Standards of 1973. 

2 Estimated based upon a range in quartz content between 
5.4 and 12.6 pet. 



derived from the American Conference of 
Governmental Industrial Hygienists Stand- 
ards of 1973 (as specified by MSHA). 
TLV's are generally based upon the time- 
weighted average exposure over a speci- 
fied time period. However, additional 
restrictions can be imposed by the maxi- 
mum excursion value, which is defined as 
the maximum allowable concentration that 
personnel can be exposed to at any time. 
Dust TLV values listed in table 1 are 
estimates based upon data published on 
the particle size of oil shale dust and 
on measurements of quartz content. The 
parameters that affect the dust TLV's 
include quartz content, respirable mass, 
and diesel particulates. Diesel particu- 
lates are counted in the total dust mass 
and the total respirable dust mass; 
they have the effect of reducing quartz 
content. This impacts the TLV, be- 
cause it is a strong function of quartz 
content. 

DIESEL ENGINE EMISSIONS 

It has been generally accepted that the 
production of nitrogen oxides (NO) and 
carbon monoxide (CO) by the large-capac- 
ity diesel loading equipment would govern 
the quantity of fresh air required at the 
face. However, studies of the production 
of diesel particulates by Breslin (1_) 5 
and Daniel (2) suggest that the require- 
ment to limit particulate concentrations 
may be the governing factor. 



Gaseous emission studies by Markworth 
(3) compared the performance of three 
engines whose peak horsepower ranged from 
800 to 1,200 hp for potential application 
to oil shale mining and illustrated that 
pollutant production rates varied over a 
large range. Emissions for the cleanest 
engine tested in the study are listed in 
table 2, along with the required quantity 
of fresh air, assuming ideal dilution. 
The required quantity of fresh air was 
determined for the additive effects of CO 
and N0 X using the inequality in this 
equation as suggested by Bossard (4): 



Ceo 



Cno, 



< 1.0 



(1) 



TLVco TLV N X 
where C = pollutant concentration, ppm. 

The tests were conducted using both 
fresh air and fresh air containing 1.5 
pet methane in the form of natural gas to 
compare emissions for nongassy and gassy 
conditions. The addition of methane pro- 
duced a large increase in CO production, 
which required an increase of ventilation 
air of 43 to 91 pet of the original quan- 
tity, depending on operating horsepower. 
The 1.5-pct methane content exceeds 
the maximum methane concentration of 1.0 
pet allowed under MSHA regulations, but 

^Underlined numbers in parentheses re- 
fer to items in the list of references at 
the end of this report. 



TABLE 2. - Comparison of engine exhaust and required ventilation 





Cone 


ppm 


Exhaust flow, 2 
ft 3 /min 


Required 


Brake horsepower 


CO 


N0 X 


ventilation, 3 
ft 3 /min 


With no methane: 

561 


100 
150 

875 
713 


488 
538 

506 
513 


1,814 
2,257 

1,830 
2,276 


36 140 


823 


55 330 


With 1.5 pet methane: 
561 


69,060 
79,170 





From Markworth (_3) for a turbocharged, after-coo 
D-348 engine with precorabustion engine and water sc 

Estimated from Markworth (3) by subtracting 
natural gas and extrapolated to 0.062 lb/ft 3 dens 
lb/ft 3 . 

Assuming ideal dilution. 



led Caterpillar 
rubber. 

mass flow of 
ity from 0.075 



illustrates that methane In the mine 
air could impact pollutant production. 
Based upon table 2, in the nongassy envi- 
ronment the engine would require 64 to 67 
ft 3 *min/bhp to meet the TLV's; in the 
gassy environment it would require 96 to 
123 ft 3 «min/bhp. 

OIL SHALE DUST AND DIESEL PARTICULATES 

Both diesel particulates and oil shale 
dust must be considered in assessing the 
impact of particulate production on face 
ventilation requirements in oil shale 
mining. Dust data reported by Volkwein 
(5_) are summarized in table 3. The aver- 
age dust mass was 1.45 mg/m 3 , and average 
quartz content was 5.8 pet. 

A group of dust measurements was re- 
ported by Brechtel (6) which included 
measurements of dust production due to 
blasting and loading operations in an 
underground oil shale mine. Dust pro- 
duced by a face blast (1,900 lb ANFO) in 
oil shale has an average total mass of 
13.2 mg/m 3 , with less than 2 pet of the 
dust having a particle diameter of less 
than 0.7 um. The dust had a light brown 
color. Particulates measured during sim- 
ulated loading operations showed that the 
fine fraction (<0.74 um) increased to 53 
to 73 pet of the total mass and was black 
in color. This led to the conclusion 
that most of the fine particles were 



diesel particulates. Quartz content 
analyses listed in table 4 support this 
conclusion in that quartz contents of the 
fine fractions were below detection lim- 
its. Quartz contents were similar in 
range to the Volkwein (5) data, averaging 
4.4 pet. 

The rates of production of respirable 
oil shale dust and diesel particulates 
are estimated in table 5, using both 
particle gradation measurements made dur- 
ing the loading and the measured ventila- 
tion flow. At an average production rate 
of 6,220 rag/min, face ventilation capac- 
ities in the range of 157,000 f t 3 /min 
would be required to maintain respi- 
rable particulates at a TLV of 1.4 mg/m 3 
(assuming 5.4 pet quartz). These mea- 
surements are probably not representative 
of expected conditons because — 

1 . The material being loaded was 
partly comprised of cuttings from a road- 
header miner and may have contained a 
disproportionately large amount of fine 
material. 

2. The diesel equipment was very old 
and poorly maintained. The generation of 
particulates during loading operations 
will be an important parameter in face 
ventilation requirements. Oil shale dust 
production must be limited by good mining 
practice such as wetting the muckpile 
and roadways, and diesel particulate 
production must be minimized by engine 



TABLE 3. - Comparison of measured respirable dust concentration 
and TLV (5) 



General location 


Alpha quartz 
content, pet 


Respirable dust, mg/m 3 




Measured cone 


TLV 1 




3.5 

14.0 

6.7 
.9 

2 2.7 
2 11.1 

NA 
2 1.8 


2.05 

NA 

2.68 
.94 

2.63 

2 1.05 

2.18 

2 .63 


1.82 


Blasting: Around corner from face. 
Scaling: 


.63 
1.15 


Mucking: 


2.00 
2.13 




.76 




NA 


Roof bolting: In or near bolter... 


2.63 




5.8 


1.45 


1.59 



NA Not available. 

'Based on quartz content. 

2 Average of values from several locations. 



TABLE 4. - Quartz content of dust sample collected during 
simulated loading operations (6) 



Loading operation 


Mass cone, 
3 
mg/m 


Quartz con- 
tent, mg/m 


Quartz as pet 


and sample type 


of total mass 


With truck shutdown: 










4.63 


0.296 


6.4 


Dichotomous sampler: 








Coarse (2.5 to 15 ym).. 


.72 


.085 


NAp 




2.34 


.030 


ND 




3.06 


.115 


3.8 


With truck idling: 




Dichotomous sampler: 








Coarse (2.5 to 15 ym).... 


.58 


.075 


NAp 




3.16 


.040 


ND 




3.74 
3.81 


.115 
.175 


3.1 




4.4 



NAp Not applicable. ND Not detectable. 

TABLE 5. - Estimated proportions of oil shale dust, diesel particulates, 
and projected production rates based upon simulated loading tests (6) 



Loading 



With truck shut down 



Worker floor 
location 



Operator 
location 



With truck 
idling 



Height above f loot ft.. 

Av dust mass, mg/m 3 : 

Total 1 

Respirable 

Oil shale dust: 

Pet of respirable mass 2 

Est production rate 3 mg/min. . 

Diesel particulates: 

Pet of respirable mass 2 

Est production rate 3 mg/min. . 

Est total respirable dust production mg/min. . 



2.8 
2.5 

21 
1,070 

79 
4,030 
5,100 



'13.2 for blasting. 

2 Assumes that total fine fraction (<0.7 ym) is diesel particulates. 

3 Based upon measured ventilation airflow of 72,000 ft 3 /min. 



12 

5.1 
3.6 

18 
1,320 

82 
6,020 
7,340 



12 

5.8 
5.1 

16 
1,660 

84 

8,740 

10,400 



selection and good maintenance in order 
to meet governing particulate TLV's. 

BLASTING 

Blast rounds planned for room and pil- 
lar operations require the detonation 
of up to 2,000 lb ANFO. Although care- 
ful control of explosive composition lim- 
its air pollutant production, studies of 
blast-produced air pollutants by Rogers 
(_7) and Abata (8) indicate that the large 
quantities of ANFO required for oil shale 



mining will produce considerable amounts 
of noxious gases. Table 6 compares esti- 
mated production to measurements for a 
full-face shot at the Colony Mine (6^). 
The table suggests that production of 
blast-produced air pollutants can be ade- 
quately predicted if the mass of ANFO 
being detonated is known. Ventilation of 
noxious gases in the face area is not 
a critical parameter after the shot, 
because personnel do not enter the head- 
ing for some time. However, if gassy 
conditions exist, methane gas may be 



liberated by face blasting and require 
implementation of special ventilation 
practices to minimize the hazard. 

METHANE OCCURRENCE IN OIL SHALE MINING 

Publicly available information on the 
occurrence of methane in oil shale sug- 
gests that it occurs both as a free gas, 
as gas in solution with groundwater, and 
as absorbed gas in solutuion with kero- 
gen. Table 7 summarizes public data on 
methane occurrence in oil shales of the 
Green River Formation. Oil shale mining 
and exploration conducted in central 
Piceance Creek Basin tracts and the 
Uinta Basin have encountered methane. 
The outcrop and erosional exposure at the 

TABLE 6. - Comparison of estimated and 
measured concentrations of gases 
produced by full-face blast at Col- 
ony pilot oil shale mine (6) 




1 Based upon Abata (8) , with a total of 
1,890 lb ANFO and an estimated dilution 
volume of 878,400 ft 3 . 

2 These concentrations would vary for 
different blasting patterns, methods of 
initiation, and fuel oil content. 

3 Includes background atmospheric C0 2 . 



southern rim apparently has allowed the 
methane to bleed off, while in the cen- 
tral Piceance Creek and Uinta Basins, 
confinement due to the hydrologic system 
may have contained the gas. 

Recent work by Sapko (9) presents the 
results of measurements of methane re- 
leased by mining operations in the Mahog- 
any Zone at the U-a, U-b oil shale lease 
in the Uinta Basin, and is particularly 
pertinent to ventilation design. Methane 
released from oil shale rubblized by 
blasting ranged from 2.3 to 22.5 ft 3 /st 
with an average value of 13.3 ft 3 /st. 
Other work by Schatzel (10) reports that 
methane given off by core samples ob- 
tained from the Mahogany Zone at C-b 
tract averaged 6.2 ft 3 /st after 125 days 
of monitoring. Total methane content of 
the core samples was not determined, but 
similar measurements by Matta (11) sug- 
gested that after 21 days of monitoring 
as much as 40 pet of the methane had been 
released. 

The deep saline oil shale sequence (Rl- 
R5 zones) found in the Central Piceance 
Creek Basin is known to have a much 
higher gas content than the oil shales of 
the overlying leached sections (R6, Ma- 
hogany [R7], and R8 zones). Data re- 
ported by Sapko (11) for saline oil 
shales rubblized by blasting indicated a 
range of 2.4 to 56.7 ft 3 /st. These data 
are not applicable to mining in the 
leached section because of differences in 
stratigraphic environment. 

Production of methane by groundwater 
entering the mine and by desorbtion from 



TABLE 7. - Summary of publicly available data on methane occurrence 
in oil shale 



Type of occurrence, by site 


Range in magnitude 
of occurrence 


Reference 




55 -1,600 
5.9 - 64.8 

2.3 - 22.5 
7.6 - 33.2 

.8 - 15.2 

.03- 32.6 

6.2 

2.4 - 56.7 


12 


Gas absorbed by kerogen, ft 3 /st: 


13 
9 




14 




15 




13 




10 




9 



the excavation boundary is expected to be 
handled by the main mine ventilation 
system. Two specific types of occur- 
rence could impact face ventilation, as 
described in the following paragraphs. 

Sudden Inflow of Methane-saturated 
Water or Free Methane 

Methane inflows could result from the 
intersection of (1) natural fractures 
that were connected to a localized aqui- 
fer with high methane saturation or 
(2) a localized reservoir of free meth- 
ane. This type of situation was reported 
by Stellavato (12) during shaft sinking 
operations at the C-b tract, where a sud- 
den inflow of water and methane produced 
initial methane release rates of 1,600 
ft 3 /min. The water inflow dropped to 13 
pet of its initial value within 24 h, and 
the methane production dropped to 55 ft 3 / 
min. There are informal reports of this 
type of methane occurrence in drilling 
operations during resource evaluation. 
The apparent randomness of occurrence 
(methane was encountered in one out of 
three shafts sunk in close proximity at 
C-b) and rapid reduction in water-meth- 
ane production encountered to date sug- 
gest small, localized reservoirs (gas 
or groundwater) , isolated from the main 
hydrologic system. In this case, the 
frequency of occurrence might be small, 
and the hazard represented would be 
reduced. 

This type of methane occurrence would 
be most hazardous if a methane layer 
developed owing to localized, high-volume 
methane flow from fractures intersecting 
the roof of a heading. Methane layering 
results when buoyant effects due to the 
density contrast between methane and air 
are of greater magnitude than the turbu- 
lent mixing energy of the airstream at a 
given velocity. 

Research on methane layering is re- 
ported in detail by Bakke (16) , who pro- 
posed "layering numbers" to evaluate the 
potential for methane layering at varying 
ventilation air velocities, methane pro- 
duction rates, and excavation widths. 
The layering number (L) is calculated by 
the equation 



L = 



37[(V/W)'/ 3 l' 



(2) 



where L = methane layering number, 

TI = ventilation air velocity, 
f t/min, 

V = methane flow rate, ft 5 /min, 



and 



W = excavation width, ft. 



This expression was developed for air 
flowing uniformly along a heading without 
any equipment to enhance mixing. Bakke 
(16) suggests that a layering number of 5 
represents an optimum for limiting the 
layer length. Further increase in air 
velocity beyond the velocity necessary to 
produce a value of 5 does not reduce 
the length of the layer appreciably. At 
layering numbers below 2, the buoyant 
effects dominate and the methane layering 
will be pronounced. 

The methane layering problem is heavily 
dependent upon the location of the meth- 
ane source and the degree of localization 
of the production. Distributing a given 
production over a long section of roof 
tends to reduce the layering problem. If 
the methane is produced from the floor or 
walls, the ventilation air can mix and 
disperse the methane more effectively. 
Bakke ( 16 ) notes that once the methane is 
well mixed in air, restratif ication due 
to the density contrast is minor. 

The magnitude of potential methane lay- 
ering problems in oil shale mining is 
difficult to estimate because of the lack 
of operating data on methane production. 
Figure 1 shows the relationship between 
methane inflow rate and required air 
velocity to achieve methane layering num- 
bers of 2 and 5. An air quantity of 
100,000 ft 3 /min for face ventilation in a 
55-ft-wide by 30-ft-high opening gives an 
average velocity of 61 f t/min. The re- 
sulting methane layering number would be 
below the critical value of 2 for methane 
inflows above 50 ft 3 /min, indicating that 
layering in the face heading area will be 
a problem given sufficient methane in- 
flow. The problem may be compounded by 
the large cross-sectional area of the 



KEY 
L Methane layering number 
W Excavation width 



c 


1 1 ' 


E 
s 


./L = 5, 


H- 


X W=55ft 


>- 




H 




5 400 


/ 


o 


/j-500,000 ft 3 /min in a 
/ ]_55- by 30-ft heading 


_i 

LU 

> 


cc 


J 


< 


f L=2, 


z 


/ W=55ft 


o 


i ^^-^ 


|= 200 


7 j**^*' 


< 


r ^^"^^^ 


_i 


1 s^"^ 


Z 


y^r-100,000 ft 3 /min in a 
"/^ J_ 55- by 30-ft heading 

i 


> 



1,000 2,000 

METHANE INFLOW, ft 3 /min 

FIGURE 1 . — Ventilation velocities required to achieve methane 
layering numbers of 2 and 5 versus methane inflow. 



openings. Ventilation using a ducted 
system results in very high velocity 
at the immediate face but relatively 
low velocity throughout the heading. In- 
creasing the average air velocity 
requires a large increase in flow rate 
through the duct, which would result in 
large energy costs. An alternative would 
be to increase local mixing by using an 
auxiliary jet fan. The use of a jet fan 
as the main face ventilation system would 
be an effective way to increase air mix- 
ing, because the jet fan uses the heading 
itself as a duct and the average air vel- 
ocity is higher (200 to 400 ft/min). 
Bakke (16) emphasizes that air velocity 
is the critical factor. 

Flow in the last open crosscut is ex- 
pected to range from 400,000 to 800,000 



ft 3 /min based upon a survey by Brechtel 
(6_) of oil shale companies. A value of 
500,000 ft 3 /min would give air velocities 
above 300 ft/min and result in a layering 
number above 2 for a quite large inflow 
of methane. 

Blast-Released Methane 

The magnitude of the methane concentra- 
tion that could result from face blasting 
in methane-saturated oil shale is diffi- 
cult to estimate because of the lack of 
definitive data on methane content and 
because of the interaction of methane 
release rate and ventilation airflow in 
the heading. Measurements of methane 
production during oil shale mining oper- 
ations at the Horse Draw facility are 
reported by Richmond (17) and Sapko (11). 
A typical curve of methane concentration 
in ventilation air after a blast (fig. 
2A) indicates that the methane concentra- 
tion reached its peak value shortly after 
the blast. Figure 2B shows a semilog 
plot of the data, illustrating the gen- 
erally linear relationship expected for 
the dilution of gas in a room of fixed 
volume ventilated by a constant flow rate 
of fresh air. Based upon room volume, 
80 pet of the total methane liberated 
by the blast was mixed with the room 
air within 5 min after the blast. Fig- 
ure 2 shows data for 60 st of blasted 
shale; it is not known how a blast 
rubblizing several thousand tons of oil 
shale would affect the rate of methane 
release. 

A typical face heading 50 ft wide by 30 
ft high, advancing 30 ft, would produce 
2,808 st of rubblized shale (density of 
approximately 124.8 lb/ft 3 ) and could 
release a large volume of methane. 
Assuming an average saturation of 13.3 
ft 3 /st, a single blast could produce 
approximately 44,000 ft 3 of methane, as 
suggested by the data from Sapko (9). 
If all the methane were released instan- 
taneously in a 50-ft-wide by 30-ft-high 
heading, 300 ft long and mixed uniformly, 
this would result in a methane concentra- 
tion of 8 pet. 



MAXIMUM LENGTH OF DEADHEADING 

Regulatory guidelines govern the length 
of the deadheading in coal mining by 
stipulating a limit of 100 ft of advance 
before breaking through a new crosscut. 
For oil shale mining, this requirement 



would be impractical. Based upon opera- 
tional considerations and typical room 
and pillar dimensions, it was estimated 
that 300 ft would be an acceptable dead- 
heading length before breakthrough to the 
last open crosscut. 



FAN SYSTEM DESIGN 



A group of seven conceptual designs of 
large-capacity face ventilation systems 
was developed as part of this study. 

The concepts were evaluated for mine 
operation compatibility, projected ven- 
tilation effectiveness, and cost. The 
highest ranking concepts were a jet fan 



— — i— i i 1 1 1 1 1 1- 

A Methane concentration in ventilating 
air after blast 




5 8.0 p B Semilog plot of gas dilution 

ul 60 

< 4.0 

X 

h- 

LU 

2 2.0 h 



1.0 
.8 
.6 



_L 



10 20 30 40 

TIME AFTER BLAST, min 



50 



FIGURE 2. — Typical curve of methane concentration in exhaust 
air after blasting oil shale in the saline zone at Horse Draw. Total 
methane = 4,088 ft 3 , which represents 60 ft 3 /st oil shale. 



system for nongassy oil shale mining and 
a reversible fan with rigid duct for 
gassy oil shale mining. 

The design of each system was based 
upon commercially available equipment. 
Each system had a common design basis, 
including 

1. 100,000-ft 3 /min capacity. 

2. Low power consumption. 

3. Components that must be handled 
with a minimum of special equipment. 

4. Two-speed operation to conserve 
power consumption when full flow was not 
needed. 

DESIGN OF THE JET FAN SYSTEM 

Jet fans (free-standing, unducted fans) 
are commonly employed in the mining in- 
dustry. The application of the jet fan 
for ventilation of a dead-end heading is 
illustrated in figure 3. The fan is 
located along the upstream corner of the 
last crosscut and projects air in a high- 
velocity turbulent jet along the wall 
toward the face. The jet expands with 
increasing distance from the fan until, 
ideally, air is flowing toward the face 
in half the opening and exhausting back 




FIGURE 3.— Schematic of dead-end heading ventilated by jet 
fan. 



10 



to the last open crosscut in the other 
half. The jet grows through the action 
of frictional forces at the boundary of 
the jet, where the relatively still air 
is accelerated or entrained into the jet. 
In this process, the initial momentum of 
the jet of air is transferred to an ever 
greater mass, thereby reducing the veloc- 
ity of flow. By the process of entrain- 
ment, the jet fan delivers a volume much 
greater than its inlet volume to the 
face, resulting in high air velocities 
and enhanced mixing. The entrained por- 
tion of the air delivered to the face is 
recirculated; therefore the dilution ca- 
pability of the jet fan is dependent upon 
the amount of fresh air entering the 
inlet. Recirculation at the inlet is 
generally 20 to 40 pet, depending upon 
inlet location. 

The key to the design of the jet 
fan system was characterization of the 
complex action of the turbulent jet. 
Although detailed analysis has been per- 
formed by Abromovich (18) , a simplified 
method derived by McElroy ( 19 ) from em- 
pirical studies was chosen for this proj- 
ect. McElroy developed a group of equa- 
tions to describe the decay in centerline 
velocity with increasing distance from 
the fan outlet. These equations are 
correlated with four phases of behavior, 
as illustrated in figure 4. For round 
jets, phases 1 and 2 are combined so that 
the jet centerline decay is predicted for 
each phase as described below. 



Gaussian air 

velocity 
distribution 



FamzE-^-yo 
Phase I and I 
2 flow I I 

fan diam) 



Phase 3 flow 
(5 to 75 fan diam) 




■Transition zone 



Phase 4 flow (beyond phase 3) 



Phases 1 and 2 

The centerline velocity, V* x , at a dis- 
tance, X, from the fan outlet is charac- 
terized by 

V x = aV , (3) 

where V Q = outlet or discharge velocity 

and a = a constant (1.0-1.2). 

The centerline velocities are fairly 
well characterized by this expression for 
a distance of up to five times the outlet 
diameter. The constant a is apparently 
related to outlet velocity, decreasing 
with decreasing velocity. 

Phase 3 

The centerline velocity, V x , at a dis- 
tance, X, from the fan outlet is charac- 
terized by 

V x = (KV D)/X, (4) 

where K = a constant (3-10), 

D = outlet diameter, 

and X = distance from the outlet. 

Phase 4 

After phase 3, a transition zone occurs 
in which the centerline velocity, V x , 
decays rapidly to the range that is 
predicted using the flow rate and one- 
half the area of the opening. After the 
transition zone, the centerline velocity 
appears to follow the equation 



V x = fV_D/109X, 



(5) 



FIGURE 4.— Plan view of freely expanding turbulent jet il- 
lustrating McElroy's different phases of velocity decay. 



where f = a constant related to the ra- 
tio of outlet diameter to 
opening dimension 

and g = 0.026f. 



11 



The constants f 
developed, with 



and g are empirically 



100 



f = 12.2 (DS)/W 



(6) 



where 



and 



S = aspect ratio of the fan outlet 
(1.0 for a round jet) 

W = large dimension of the 
opening. 



McElroy's equations were developed for 
jets expanding freely in all directions. 
Placement of the fan along the wall, 
as illustrated earlier in figure 3, 
constrains the growth of the jet and 
increases the distance in which phase 3 
behavior is observed. This is incorpo- 
rated into the predictive equation 3 by 
increasing the value of the constant K. 

McElroy's (19) equations are similar to 
work reported by Krause ( 20 ) and were 
checked by fitting the relationships 
to experimental data from Lewtas ( 21 ) 
and Spendrup (22). K values were found 
to vary between 5.0 and 11.3 for fans 
located within three fan diameters from 
the wall. Distance from the fan outlet 
to the transition zone was found to be an 
approximately linear function of outlet 
velocity divided by discharge diameter, 
as shown in figure 5. 

The zone of the heading that is of 
critical importance in mining applica- 
tions is the transition zone and beyond. 
At this point, the entrainment action in- 
creases rapidly, causing a rapid decrease 
in flow velocity. The design process 
must ensure that the jet can force air to 
the face with sufficient velocity to 
provide good mining and face sweep. 

Application of the design equations was 
compared to field measurements for a 39- 
in-diam fan tested at Union Oil Co. of 
California's Parachute Creek shale oil 
project by Spendrup (22). Figure 6 shows 
good correlation of the predictive equa- 
tions and measured data near and beyond 
the transition zone. 

Design of a jet fan for this work was 
based upon the following: 




y=0.0064 X+40.7 
1**0.75 



2,000 4,000 6,000 8,000 

OUTLET VELOCITY / DISCHARGE DIAMETER 
(Vo/D), ft.mln/ft 

FIGURE 5.— Approximate distance to transition zone (phase 
4 flow) as a function of outlet velocity normalized to outlet 
diameter for fans located adjacent to a wall. 



I ' I 
KEY 
Fan diam = 39 in 
Outlet vel = 6,800 ft/min 
Flow rate =56,760 ft 3 /min 
• Measured data 
Predicted 




25 50 75 

DISTANCE/ FAN DIAMETER (X/D) 



100 



FIGURE 6.— Jet fan penetration versus velocity curve for large 
jet fan tested in oil shale mining. 

1. Flow capacity based upon expected 
rates of pollutant emissions at the face. 

2. Fan diameter selected such that the 
jet reaches the face with 100-ft/min 
velocity. 

Using K = 5.0, a flow rate of 100,000 
ft 5 /min, and opening dimensions of 55 ft 
wide by 30 ft high, fans with diameters 
between 48 and 60 in were predicted to 
project air in the range of 300 ft with a 



12 



minimum velocity of 100 ft/min. Based 
upon this, a 55-in-diam fan was selected. 

DESIGN OF THE DUCTED FAN SYSTEM 

Design methods for ducted fan systems 
are described elsewhere by Hartman (23) , 
Jorgensen (24), and Daly (25). The pri- 
mary design concerns in this work were 
whether to use a blowing or exhausting 
system and the size of ducting needed 
to optimize power consumption yet allow 
handling without special equipment. 

A reversible system was selected for 
this work to establish a relative compar- 
ison between blowing and exhausting ven- 
tilation. This selection required rigid 
duct, and from practical considerations, 
it appeared that 54-in-diam round or 62- 
by 40.5-in oval ducts were as large 
as could be handled conveniently by a 
two-member crew without specialized 
equipment. This size was also a practi- 
cal minimum, since a system ventilating a 
distance of 300 ft would be operating at 
approximately 5.0-in-wg total pressure, 
requiring around 120 hp. 

Operation of this type of system for 
ventilation of a dead-end heading is 
illustrated in figure 7, for both blowing 
and exhausting modes. Positioning of the 
inlet is a critical parameter in elim- 
inating recirculation. In the blowing 
mode, the inlet should be around the cor- 
ner and upstream in the last open cross- 
cut. For the exhausting mode, this sys- 
tem was designed to project the jet of 



Fresh 
air 



320 ft 






■A 



Rigid duct 



Reversible 
ventilation fan 



'^ 



mmmmm 



J 



DUCTED FAN- BLOWING MODE 



Fresh 
air 



320 ft 



Rigid duct 



* 



^ 



/— Kigia auci 



_ Reversible 
ventilation fan 



*) 



I \ 



DUCTED FAN- EXHAUST MODE 



FIGURE 7.— Schematics of the ducted fan system operating 
in dead heading. 

exhaust air downstream but across the 
opening of the deadheading. The high 
velocities of the jet were expected to 
minimize recirculation of the exhaust 
air. If this approach were unsuccess- 
ful, exhaust mode operations would have 
to utilize auxiliary ducting at the roof 
to carry the exhaust downstream past the 
opening. This would require a more com- 
plicated dampered control system with 
a branching duct to pass the exhaust 
duct up along the roof to the downstream 
side of the face heading in such a way 
that it did not interfere with mine 
traffic. 



APPLICATIONS OF TRACER GAS TESTING RESULTS 



Sulfur hexafluoride (SF 6 ) tracer gas 
was used to measure the average per- 
formance of the face ventilation systems. 
Different models of tracer gas release 
were designed to simulate the production 
of diesel emissions, blast fumes, and 
methane in the face area. Measurements 
of the tracer gas concentration through- 
out the room, and especially in the face 
area, provided data on the uniformity 
of mixing and the average ability of 
the systems to dilute air pollutants. 
These tests were described in detail by 
Brechtel (6). 



The results of the tracer gas testing 
are compared using a uniform measure of 
the efficiency of the face ventilation 
system, called dilution efficiency. For 
a perfect system, all of the air passing 
through the fan would be uniformly mixed 
with all of the tracer gas released in 
the face area. The resulting dilution 
efficiency would equal 1.0. Dilution ef- 
ficiency is calculated using equation 7: 



E d = Qe /Of » 
where E d = dilution efficiency, 



(7) 



13 



Q E = quantity of air actually ven- 
tilating the room, as mea- 
sured by tracer gas dilu- 
tion, ft 3 /min, 



and Q F = measured outlet flow rate 
the fan, ft 3 /min. 



of 



In an actual mining situation, the 
value of the dilution efficiency would be 
less than 1 .0 because of recirculation, 
efficiency of mixing at the pollutant 
source, turbulence, last open crosscut 
flow, and measurement error. The tracer 
gas tests measured the combined effects 
of these parameters and allowed these 
effects to be accommodated in the design 
of ventilation capacity. 

TRACER GAS DETERMINATION OF 
DILUTION EFFICIENCIES 

The tracer gas tests were conducted in 
Exxon's Colony pilot mine in crosscut 7, 
shown in figure 8. The mine ventilation 
system was capable of supplying 124,000 
ft 3 /min of fresh air, and a brattice wall 
channel was constructed to bring the air 
past the test room at velocities between 
250 and 300 ft/min. The test room was 
nominally 55 ft wide by 30 ft high and 
was closed at a depth of 320 ft by a 



Brattice 






wall 

LEGEND 
Fresh air 


\<X 


/&^ Brattice wall 


Exhaust air 

Full-height extraction (60 ft) 

Pillar numbers 


/% 


S\ ^^_ Brattice 
)*v\ wall channel 



e 



/(- 






PI 



Fan 3 
(exhaust) 



&£>t 



5® 



Fan 2 
2 48-in rigid ducts 



£2 



Scale, ft 



FIGURE 8.— Schematic of Colony Mine showing mine ventila- 
tion system and location of test room in crosscut 7. 



brattice wall constructed on top of an 
existing muckpile. 

The tracer tests were designed to simu- 
late different types of mine air pollu- 
tant production. The tests included — 

Simulation of blast clearing . — This 
test was designed to simulate the fan's 
effectiveness at clearing a heading after 
blasting. The test room was sealed, and 
SF 6 gas was released to give a uni- 
form concentration of approximately 1 
ppb. The fan was run for a short time to 
mix the gas uniformly. The mine ventila- 
tion system was then started, and the 
fans were used to clear the tracer gas 
from the room. 

Simulation of hot diesel exhaust . — Thi s 
test was designed to simulate the sys- 
tem's ability to dilute diesel emissions 
(gaseous and particulates). A 50,000- 
Btu/h kerosene space heater was placed in 
the face area, with the exhaust routed 
through a vertical stack to be released 
15 ft above the floor. Tracer gas flow- 
ing at a constant rate was mixed in the 
hot gas stream before the outlet. The 
space heater generated a stream of hot 
gases with a buoyancy similar to that 
of engine emissions. The mine venti- 
lation and face ventilation systems were 
started, and the steady-state concentra- 
tion for SF 6 was measured. 

Simulation of methane layering . — SFg 
was mixed with 52.4 mol pet He in air to 
simulate the density of methane gas. It 
was released from very small holes along 
a 50-ft-long pipe that was suspended at 
the roof. The pipe would simulate the 
intersection of a crack that is conduct- 
ing methane gas into the mine at roof 
level, with the lighter density of the 
mixture causing the tracer gas to form a 
layer similar to methane. The tracer gas 
was released at a rate of 0.833 ft 3 /min 
for 120 min, and gas samples were taken 
to see if the tracer would form a roof 
layer similar to that formed by methane. 
The fans were then started to test their 
effectiveness at breaking up the layer. 

Simulation of methane emissions from a 
muckpile . — In this test, the mixture of 
air, helium, and SF 6 was released from 
a group of pipes laid out in the face 



14 



area to simulate methane desorbing from 
freshly blasted muckpile. The tracer gas 
was released for 45 to 60 min, and then 
the fans were started. The steady-state 
concentration was measured to establish 
the effectiveness of the two systems. 

Measurement of fan inlet recircula- 
tion . — The inlet recirculation volume was 
measured by releasing tracer gas directly 
into the fans. The concentration in the 
air around the inlet was measured. The 
concentration of air coming out the fan 
is governed by the release rate of the 
tracer gas and the amount of tracer gas 
recirculated into the outlet. 

Figure 9 shows a schematic of the mea- 
surement grid established in the test 
room and illustrates the location of 
the fans during the testing. Figure 10 
shows the sampler locations used during 
each type of tracer gas test. Identical 
tracer gas concentrations, tracer gas 
release rates, and sampler locations were 
used for each fan in each type of test to 
assure that the results would be directly 
comparable. 

TEST RESULTS 

Dilution efficiencies measured during 
the tracer gas tests are compared in 
table 8. Tests were not repeated 
because of the extensive setup required; 
therefore, there is no measure of the 
reproducibility of the data. In one in- 
stance, a tracer gas of the wrong con- 
centration was released, requiring a 



\ 



320 300 280 260 



Scole, ft 

200 ISO 



100 60 60 40 20 3 



V. 



PLAN VIEW 



c '/t^i\t-rrfi\<rrm^\\^te 



•t u r- 






ia>/»a-»am/mia» 



ELEVATION 



Muckpile — ' 



Js iL JJJ iL J 



z) 



V 



y^ 



-J 



_l 






Ducted fan-blowing mode Ducted fan-exhaust mode 



FIGURE 9.— Test room grid system showing location of fans 
during tracer gas tests. 



repetition of the test. Dilution effi- 
ciencies for the two tests were 0.80 and 
0.83, even though the concentration of 
SF 6 in the released gas differed by a 
factor of 1,000. The average values 
listed in the tables are mean values of 
the dilution efficiencies measured at 
each sample point throughout the test 
room. The values for the face area are 
averages of the samples located 40 to 60 
ft from the face. The jet fan delivered 
superior performance in the diesel ex- 
haust and methane from muckpile tests. 
The ducted system was superior in the 



TABLE 8. - Comparison of dilution efficiencies measured in 
tracer gas tests 



Simulation type 



Jet fan 
(88,400 ft 3 /min) 



Ducted fan, 
blowing 
(90,700 ft 3 /min) 



Blast clearing: Average.. 
Diesel exhaust: 

Face area 

Average 

Methane layering: 

Face area 

Average 

Methane from muckpile: 

Face area 

Average 

1 0.79 in exhausting mode (7 




0.98 

.63 

.74 

.77 
.83 

.59 

.60 



3,000 ft J /min) 



15 




10ft 
15 ft 



HOT EXHAUST TEST 



KEY 
Sampling station 




Tracer gas discharged 

from pipe at roof 

Station 

3 



ffLlOft 

u 15 " 



METHANE LAYERING TEST 



Station 
3 





BLAST CLEARING TEST 



10 ft 
15 ft 
25ft-jf 

METHANE FROM MUCKPILE TEST 



FIGURE 10.— Schematic showing tracer gas sampling points 
and tracer gas release point for various simulations. 



blast clearing and methane layering 
tests. The overall performance of both 
systems was good, and the data indicate 
that the fans provided effective 
ventilation. 

The methane layering test showed that 
the helium-air mixture could be used to 
simulate the buoyancy of methane. Both 
fan systems were effective at breaking up 
the tracer gas layer; however, the flow 
rate of the gas was very small (0.83 ft 3 / 
min) . Much larger release rates would be 
needed to gauge the effectiveness of the 
jet fan and ducted fan in dealing with 
significant flow rates of methane. The 
ducted systems appear to have been more 
effective at breaking up the tracer gas 
layer. This is due mostly to the fact 
that the duct outlet delivered the fresh 
air at high velocity directly at the 
point of tracer gas release. 

IMPACT OF FAN RECIRCULATION 

Inlet position and conditions are im- 
portant because they govern the amount 
of inlet recirculation. The field char- 
acterization of the test systems was 
conducted in a manner that would re- 
flect real operating conditions. Inlet 



recirculation measurements were performed 
using the tracer gas and showed 
recirculation volumes of 23.8 and 28.4 
pet for the jet fan and ducted fan, 
respectively. The jet fan value was 
typical, but the ducted fan value was 
higher than expected. The ducted fan 
recirculation was caused by poor posi- 
tioning of the inlet. The fan should 
have been placed farther upstream in the 
last open crosscut to eliminate recircu- 
lation. Inlet recirculation is expected 
with the jet fan, but care must be taken 
to locate the fan inlet as far into 
the last open crosscut as possible to 
maximize performance. Efficiency of the 
jet fan could be further increased by 
flexible ducting on the inlet placed well 
upstream in the last open crosscut. 

Dilution efficiencies corrected for the 
inlet recirculation are compared with the 
measured values in table 9, which shows 
that inlet recirculation has a strong 
effect in the reduction of dilution effi- 
ciency in these tests. 

IMPACT OF FAN OUTLET LOCATIONS 

Positioning of the jet fan is critical 
to its performance. Previous work by 
Lewtas (21) and Dunn ( 26 ) indicates that 
location of the fan within three 
diameters of the wall extends the depth 
of penetration of the jet by constraining 
its growth. Anemometer and smoke veloc- 
ity measurements were made for several 
different directions and heights of the 
fan centerline. Results, listed in table 
10, indicate that the fan had its great- 
est penetration when angled slightly down 
and into the corner. Directing the flow 
into the corner at too great an angle 
reduces penetration by causing the air 
to bounce off the adjacent wall. Wall 
roughness was probably a factor in this 
problem. Elevating the fan above the 
corner caused a large reduction in pene- 
tration and velocity. 

Position of the duct outlet has been 
shown to have a major effect on the per- 
formance of ducted systems in the exhaust 
mode. Measurements of the effect of dis- 
charge location on the ducted system were 
made in this study to evaluate the effect 
of positioning for the blowing mode. 



16 



TABLE 9. - Potential increase in dilution efficiency resulting from 
elimination of inlet recirculation 



Simulation type 


Jet fan 
(88,400 ft 3 /min) 


Ducted fan, blowing 
(90,700 ft 3 /min) 




With 
recirculation 


Without 
recirculation 


With 
recirculation 


Without 
recirculation 


Diesel exhaust: 


0.71 
.78 

.57 
.59 

.74 
.79 


0.87 
.97 

.80 
.82 

.90 
.96 


0.63 
.74 

.77 
.83 

.59 
.60 


0.81 


Methane layering : 


.98 
1.0 


Methane from muckpile: 


1.0 

.86 




.89 



TABLE 10. - Locations, orientations, and face air velocities for jet fan 



Peak velocity, 2 ft/min 



Test 



Distance 

from face, 

ft 



Height 

above 

floor, 

ft 



Orientation 

in vertical 

plane, ft 



Angle from 

axial section — 

line A 



At 100 ft 
from face 



At 60 ft 
from face 



306.7 
306.7 
305.5 
305.5 
305.5 
305.5 
305.5 



8.5 
17.3 
3 4.0 
3 3.4 
3 3.7 
3 3.7 
3 3.9 



Level 

1 • *uOi •••••••• 

• • •QUt •••••••• 

Down 5° 

Down 2-1/2°... 

Down 1 ° 



0° 

0° 

0° , 

Left 5° 

Left 2-1/2' 
Left 1°..., 
...do 



557 
170 
717 
522 
690 
618 
726 



NA 

NA 
489 

NA 
439 

NA 
550 



NA Not available. 

'All tests were run with fan located 18.4 ft left of the room centerline. 

2 Measured in lower left-hand quadrant of room cross section. 

3 Fan removed from scissors lift and mounted on blocks on the floor. 



TABLE 11. - Duct discharge locations and face sweep velocities 
for ducted fan — blowing 



Discharge 


Offset 


Height of duct 


Discharge 


Average face 


distance 


from room 


centerline 


duct 


sweep velocity, 


from face, 


centerline, 


above floor, 


section 


ft/min 


ft 


ft 


ft 






58.3 


20.9 


2.5 


54-in-diam round.. 


NA 


30.5 


21.0 


2.6 




532 


30.5 


21.0 


2.6 




456 


78 


21.0 


13.0 




1,095 


NA Not ava 


ilable. '62 


by 40.5 in. 


55.8 by 36.5 in. 





Results are listed in table 11. The 
highest face sweep velocities were 
observed with the duct centering elevated 
13 ft above the floor and the discharge 
78 ft from the face. This position was 
selected as the minimum distance at which 



a rigid duct system run along the floor 
could escape destruction during blasting. 
Face blasting at the Colony Mine threw 
a great deal of rubble along the floor 
for several hundred feet. Ducting run 
along the roof very close to the face 



17 



suffered no damage during the same blast. 
Installation of large, rigid ducting 
along the roof would be more labor inten- 
sive, and the floor installation appeared 
to be a more desirable approach from the 
operating standpoint. 



The methane layering simulation illus- 
trated the potential utility of being 
able to orient the duct outlet so that 
high-velocity flow can be directed at 
localized pollutant production. 



CASE STUDIES OF PERFORMANCE IN PROJECTED OPERATING CONDITIONS 



The primary advantage of performing 
tracer gas tests to characterize the 
performance of a face ventilation system 
is that the actual dilution efficiency of 
the system is measured at the point of 
maximum pollutant production. Once the 
efficiency is known, the total air capac- 
ity required to ventilate a known rate 
of pollutant production can be calcu- 
lated using the efficiency factor and 
assuming linearity. Dilution efficien- 
cies measured during the in-mine tests in 
this project were applied to the examples 
of projected mine air pollutant produc- 
tion discussed earlier. This illustrates 
the application of the results of the 
tracer gas tests and evaluates the capa- 
bility of the two ventilation systems to 
perform under actual mining operation. 



The dilution efficiency is the ratio 
of the air quantity delivered to the 
face divided by the fan outlet volume. 
Therefore, the dilution efficiency (E d ) 
multiplied by the fan flow rate is 
approximately the effective flow (Qq). 
For a given room volume (V) , the time to 
reach TLV is given by equation 8: 

T = (V/Qb) (lnC - In TLV), (8) 

where T = time to reach TLV, min, 

Qq = effective flow rate = E d 
x Q Fan , ft 3 /min, 

V = room volume, ft 3 , 

and C = peak concentration, ppm. 



BLAST-PRODUCED POLLUTANTS 

Projected versus measured blast-pro- 
duced air pollutant levels were presented 
earlier in table 6. The dilution effi- 
ciencies measured in the blast clearing 
tests can be used to calculate the time 
to reduce the concentrations of noxious 
gases after the blast to their TLV's. 



Table 12 lists estimated times for the 
fan systems tested in this study to ven- 
tilate the test room to TLV's for various 
blasting fumes. The peak concentrations 
are those observed in measurements of 
blasting fumes produced by face blasting 
at Colony. The maximum time of 20 min to 
clear the dust is clearly acceptable from 
an operating standpoint. 



TABLE 12. - Estimated time to clear blast-produced 
pollutants to TLV's 



Pollutant 


Est cone after 
blast, ppm 


TLV, 
ppm 


Time to dilute to TLV, 1 min 




Jet fan 2 


Ducted fan-blowing 3 


co 2 

Dust 4 . . .. 


450 
155 

69 

69 

13.3 


5,000 

50 

25 

25 

1 


NAp 
8.8 
7.9 
7.9 
20.1 


NAp 
6.6 
5.9 
5.9 

15.0 



NAp Not applicable. 
'Room volume (V) = 514,600 ft 3 ; Q e = E d 
2 Q Fan = 88,400 ft 3 /min; E d = 0.75. 
3 Q Fan = 90,700 ft 3 /min; E d = 98. 
4 Approximate; based on weight. 



Qf ; 



18 



DIESEL EMISSIONS 

Dilution efficiencies measured during 
the tracer testing can be used to esti- 
mate the actual air volumes the fan must 
move in order to dilute the diesel emis- 
sions in the face area to TLV. Earlier 
engine emissions measured on a clean die- 
sel engine in the 1,000-hp range were 
listed to obtain projected ventilation 
requirements. Actual fan flow rates can 
be estimated by dividing the ideal air 
requirements by the dilution efficiency. 

Table 13 compares the ventilation 
requirements based upon the combined 
effects of CO and N0 X . Based upon the 
engine emissions data and the measured 
dilution efficiencies, the jet fan system 
can effectively maintain the regulatory 
air quality with 95 to 98 ft 3, min/bhp 
in a nongassy mining environment. The 
ducted fan in the blowing mode would 
require 107 to 110 ft 3, min/bhp. This 
assumes the use of modern, clean-operat- 
ing, and well-maintained diesel engines. 
If this is not the case, then the venti- 
lation requirements will increase signif- 
icantly. The ventilation air require- 
ments would also be strongly affected if 
methane concentrations in gassy mining 
conditions are high enough to impact en- 
gine carbon monoxide production. At 1.5 
pet methane, which is greater than the 
maximum allowable operating concentra- 
tion, the ventilation requirements would 
be increased to 136 to 173 ft 3, min/bhp 



for the jet fan system and to 153 to 195 
ft 3, min/bhp for the ducted fan system. 

Data on diesel particulate emissions 
are not definitive. In general, Bran- 
stetter's (27) results suggest that die- 
sel particulate emissions will not be a 
problem with clean-burning, well-main- 
tained engines. 

The tracer gas measurements included 
the effect of the buoyancy resulting 
from engine exhaust temperature; however, 
tracer flow rates in these tests were 
well below the exhaust flow rates for 
diesel engines in the 500- to 1,000-hp 
range. Stratification would be a func- 
tion of pollutant flow rate, as in the 
case of methane layering; however, in 
this case, stratification may help main- 
tain air quality at the operator's level 
by concentrating the pollutants near the 
roof. 

METHANE EMMISSIONS 

Projection of the type and magnitude of 
problems that may occur in oil shale min- 
ing under gassy conditions is difficult 
because there are few published data on 
methane occurrence. Available data sug- 
gest that methane production during min- 
ing in the Mahogany Zone may occur in the 
Central Piceance Creek and Uinta Basins; 
however, the degree of methane saturation 
appears to be well below that found 
in many operating coal mines. The large 
size of openings planned in oil shale 



TABLE 13. - Comparison of required fan outlet flow rates (assuming 
clean-burning diesel engine in the 800-hp range) 



Brake 


Cone in exhaust, ppm 


Exhaust flow, 
ft 3 /min 


Ventilation flow, ft 3 /min 


horsepower 


CO 


N0 X 


Ideal 1 


Actual 




Jet fan^ 


Ducted fan 3 


With no methane: 
561 


100 
150 

875 
713 


448 
538 

506 
513 


1,814 
2,257 

1,830 
2,276 


36,140 
55,330 

69,060 
79,180 


54,990 
77,910 

97,270 
111,520 


61,970 


823 


87,810 


With 1.5 pet 
methane: 
561 


109,620 




125,680 



'Calculated using equation 1. 

2 Dilution efficiency in face area = 0.71. 

3 Dilution efficiency in face area = 0.63. 



19 



mining tends to create greater potential 
for methane layering problems. This is 
offset somewhat by the large ventilation 
air requirements imposed due to the die- 
sel loading and hauling equipment. 

The tracer gas simulations of methane 
layering and methane from the muckpile 
indicated that roof layering in large 
openings without ventilation would be a 
potential problem. Both the jet fan and 
the ducted fan were effective in break- 
ing up the roof layer and in reducing 
the tracer concentration at very low 
tracer flow rates. Work by Bakke ( 16 ) on 
methane layering predicted that the 
tracer gas layer would be broken up at 
operating flow rates of the two fan sys- 
tems because of the very low flow rates 
of the tracer gas. Further testing at 
higher tracer gas flow rates using the 
helium-air mixture would provide a poten- 
tial tool for extrapolating the currently 
available work on methane layering num- 
bers to oil shale mining. 

The most clearly identified problem 
associated with methane occurrence in 
oil shale mining is the release of the 
gas from a blasted muckpile. It was 
estimated earlier that methane concentra- 
tions of 8 pet could occur in a 300-ft- 
long heading as a result of a face blast. 
Clearly, this estimate Is directly de- 
pendent upon the assumed methane satura- 
tion (13.3 ft 3 /st), which is not well 
defined. Other parameters that would 
affect the peak concentration include — 

1. The assumption of instantaneous re- 
lease of the methane. 

2. The volume of the room. 

3. The containment of all of the 
methane in the room. 

Observations developed from work per- 
formed on this project tend to support 
the assumptions listed above. Blasting 
fume concentrations measured in a face 
blast at Exxon's Colony Mine were close 
to projected values based upon the mass 
of ANFO detonated and the volume of the 
heading (55 ft wide by 30 ft high by 
465 ft long). The fumes were vertically 
stratified, but tended to be uniformly 
distributed throughout the length of the 
room. The fumes generally were contained 
in the room until ventilation was begun. 



Measurements of methane produced by 
blasting of saline zone oil shale (11) 
suggest that 80 pet of the total methane 
produced by the blast had been released 
within 5 min. 

If the methane released by blasting 
produces very high initial concentrations 
in the face heading, the operator will be 
required to implement special procedures 
to eliminate the hazard. These might 
include — 

1. Reducing the size of the individual 
blast to reduce the quantity of methane 
released. 

2. Increasing the quantity of fresh 
air flowing in the last open crosscut. 

3. Implementing special ventilation 
procedures in the face heading. 

The quantity of methane released by a 
particular blast could be reduced by 
reducing the depth of blastholes. This 
approach may be undesirable, since the 
economic aspects of oil shale mining 
require maximum productivity. 

The tracer gas tests performed In this 
study indicated that the concentration 
of a blast-produced air pollutant being 
exhausted from the face area is instanta- 
neously equal to the general concentra- 
tion throughout the room. If the initial 
concentrations of methane are very high, 
operation of the face ventilation system 
pushes methane into the last open cross- 
cut at a high rate initially. The rate 
decays as the concentration of methane in 
the face area is reduced. If the face 
ventilation system is to be operated at 
high capacity, the last open crosscut 
flow must be capable of diluting the 
initial methane production to a safe 
level. Planned open crosscut flows might 
have to be increased, depending upon the 
magnitude of methane saturation. 

Another alternative is to control the 
rate at which the methane is removed from 
the face, so that the quantity of fresh 
air in the last open crosscut is 
always enough to dilute the methane to a 
safe level. This could be accomplished 
by operating the ducted system at a 
reduced flow rate in the blowing mode, as 
illustrated in figure 11. This configu- 
ration might be enhanced by using a jet 
fan blowing parallel to the last open 



20 



Last open 
crosscut 



Jet fan 



~Dsc 




Face 



Plume of exhaust air 



FIGURE 1 1 .—Ducted system operating in blowing mode with 
jet fan to assist methane plume mixing. 



Last open crosscut 



4^" 



Jet fan 



MM 



\ 



r 



FIGURE 12.— Reorientation of jet fan to minimize inlet recir- 
culation and reduce effective room airflow rate for methane 
dilution. 



crosscut (with or counter to the flow) to 
enhance mixing of the plume of exhaust 
gas. 

Proposed rules recently published in 
the Federal Register ( 28 ) clarify and re- 
vise MSHA's existing standards for gassy 
metal and nonmetal mines. They specify 
that auxiliary fans shall be operated so 
that recirculation is minimized, which 
may make the use of jet fans possible in 
gassy conditions. A jet fan could be 
repositioned so that it projects the air- 
stream across the room, as illustrated in 
figure 12. This would reduce both the 
effective flow rate of air in the room 
and the quantity of methane reaching the 
last open crosscut. 



The jet fan might be left running 
during the blast. This could help to 
reduce the magnitude of the peak concen- 
tration reached in the face heading. The 
overall effectiveness of this approach is 
unknown, because it is a function of the 
methane release rate. However, if the 
buildup to peak concentration occurs in 
about 5 min, a large portion of the 
methane could be removed during the 
initial release period. This would sig- 
nificantly reduce both the magnitude of 
peak concentration and the level of the 
hazard that the methane presents. 



GENERAL CONCLUSIONS ON FACE VENTILATION 



Major conclusions derived from the 
field testing of two of the large-capac- 
ity face ventilation systems follow: 

1. Face air quantities generally will 
be governed by the requirement to main- 
tain air quality TLV's. 

2. Control of particulate concentra- 
tions will be a critical parameter in the 
design of face ventilation systems. 

3. Both face ventilation systems 
showed high dilution efficiencies and 
were effective in ventilating the face 
area at a distance of 320 ft. 



4. Proper positioning of fan inlets to 
minimize recirculation directly impacts 
the ventilation performance. For both 
the jet fan and the ducted fan, the inlet 
should be placed as far as possible into 
the last open crosscut. Flexible duct- 
ing on the fan inlet side, which runs 
upstream in the last open crosscut, would 
also greatly reduce recirculation. Fan 
inlet recirculation probably reduced the 
dilution efficiencies between 17 and 27 
pet in these tests. 



21 



5. Overall performance of the two sys- 
tems was similar. The ducted system 
performed better in the blast clear- 
ing and methane layering tests. The jet 
fan performed better in the hot diesel 
exhaust and methane from muckpile tests. 

6. The superior performance of the 
ducted fan in the methane layering test 
was due to the fact that its outlet was 
very near the source of the tracer gas. 
This emphasized the fact that high air 
velocity is the critical parameter in 
controlling layering. 

7. Both systems, in the blowing mode, 
were effective at breaking up a tracer 
gas layer formed with low tracer gas flow 
rates. Further simulations at higher 
flow rates are required to extrapolate 
the capability of the system in dealing 
with layering. 

8. The jet fan provides a higher aver- 
age air velocity throughout the heading. 
This high velocity would tend to make the 
jet fans more effective in breaking up 
methane layers than a ducted system, al- 
though the background concentration of 
methane might be higher because of higher 
fan inlet recirculation. 

9. Based upon power consumption per 
effective cubic foot per minute of air- 
flow, the jet fan delivered similar per- 
formance with less power consumption than 
the ducted system. 



10. The jet fan was more efficient at 
a flow rate of 60,000 ft 3 /min than at 
88,400 ft 3 /min and delivered similar di- 
lution rates at both rates. This sug- 
gests some interaction between the turbu- 
lent jet and room dimensions that is not 
well understood. 

11. Operation of the ducted fan in 
the exhaust mode reduced its dilution 
efficiency by 19 pet as compared to 
efficiency using the blowing mode. 

12. The ducted fan tests indicate that 
the blowing mode operation is more 
efficient than the exhaust mode in the 
large openings found in oil shale min- 
ing; however, the exhuast mode might 
be more effective in situations with 
high dust production. Overall cost and 
installation labor could be reduced by 
using collapsible ventilation tubing and 
operating the fan in the blowing mode 
exclusively. However, collapsible tubing 
has disadvantages, including being prone 
to leakage, being more easily damaged, 
and having its cross section reduced by 
bends or external obstructions. 

13. The design capacity of the fan 
systems (100,000 ft 3 /min) will be suf- 
ficient for room and pillar mining opera- 
tions in oil shale, provided that diesel 
engines with low emissions are used. 
Operation of these engines in a gassy 
environment may require an increase in 
ventilation air requirements. 



REFERENCES 



1. Breslin, J. A., A. J. Strazisar, 
and R. L. Stein. Size Distribution and 
Mass Output of Particulates From Diesel 
Engine Exhausts. BuMines RI 8141r, 1976, 
10 pp. 

2. Daniel, J. H. , Jr. Diesels in Un- 
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3. Markworth, V. 0., and C. D. Wood 
III. Large Diesel Engine Testing for 
Oil Shale Mining (contract J0265023, 
Southwest Res. Inst.). BuMines OFR 2-79, 
1978, 98 pp.; NTIS PB 291 585/AS. 

4. Bossard, F. C, J. J. LeFever, 
J. B. LeFever, and K. S. Stout. A Manual 
of Mine Ventilation Design Practices. 
Floyd C. Bossard and Associates, Inc., 
Butte, MT, 1983, pp. 6-1 to 6-5. 



5. Volkwein, J. C, and P. F. Flink. 
Respirable Dust Survey of an Underground 
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6. Brechtel, C. E., M. E. Adam, and 
J. F. T. Agapito. Development of Effec- 
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Agapito and Associates). BuMines OFR I4- 
86, 1985, 146 pp.; NTIS PB 86-159829. 

7. Rodgers, S. J. Analysis of Toxic 
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Bunting, and J. Robb. Monitoring of 
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Explosives Tested in an Underground Mine 
Cgrant GO 177 130, MI Technol. Univ.). 



11987 



i'7 



22 



BuMines OFR 44-79, 1978, 99 pp.; NTIS PB 
295 676. 

9. Sapko, M. J., E. S. Weiss, and 
K. L. Cashdollar. Methane Released 
During Blasting at the White River Oil 
Shale Project. Paper in Nineteenth Oil 
Shale Symposium Proceedings. CO Sch. 
Mines, Golden, CO, 1986, pp. 59-68. 

10. Schatzel, S. J., D. M. Hyman, and 
A. Sainato. Case Study of Methane Occur- 
rence in the Cathedral Bluffs Shale Oil 
Mine, Colorado. Paper in Nineteenth Oil 
Shale Symposium Proceedings. CO Sch. 
Mines, Golden, CO, 1986, pp. 38-46. 

11. Sapko, M. J., J. K. Richmond, and 
J. P. McDonnel. Continuous Monitoring of 
Methane in a Deep Oil Shale Mine. Paper 
in Fifteenth Oil Shale Symposium Proceed- 
ings. CO Sch. Mines, Golden, CO, 1982, 
pp. 320-340. 

12. Stellavato, N. Results of the 
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Sinking and Subsequent Station Develop- 
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13. Shell Oil Co. Oil Shale Tract 
C-b, Environmental and Exploration Pro- 
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available from Area Oil Shale Office, 
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14. Matta, J. E., J. C. LaScola, and 
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15. Smolniker, H. M. Preliminary Re- 
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Area Oil Shale Office, Minerals Manage- 
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16. Bakke, P., and S. J. Leach. Prin- 
cipals of Formation and Dispersion of 
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17. Richmond, J. K. , M. H. Sapko, 
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Shale Mines. Paper in Fourteenth Oil 
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18. Abromovich, G. N. The Theory of 
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19. McElroy, G. E. Air Flow at Dis- 
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1943, 30 pp. 

20. Krause, D. Freistrahlen bei der 
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21. Lewtas, T. A. Assessment of In- 
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22. Spendrup, J. Private Communica- 
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23. Hartraan, H. L. Mine Ventilation 
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24. Jorgensen, R. Fan Engineer Inc. 
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25. Daly, B. B. Wood's Practical 
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26. Dunn, M. F., F. S. Kendorski, 
M. 0. Rahim, and A. Mukherjee. Test- 
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J0318015, Engineers International). Bu- 
Mines OFR 106-84, 1983, 132 pp.; NTIS PB 
84-196393. 

27. Branstetter, R. , R. Burrahm, and 
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195528. 

28. Federal Register. U.S. Mine Safe- 
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June 4, 1985, pp. 23,612-23,660. 



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